Nonaqueous electrolyte batteries in which charge/discharge is performed when lithium ions are transferred between a negative electrode and a positive electrode are studied as a high energy density battery.
These nonaqueous electrolyte batteries are expected to be used as not only electrical power sources of mobile devices but also or large-scale electrical power sources such as automobile and stationary power applications. In such large-scale applications, life properties and high safety are required.
For positive electrode active materials of nonaqueous electrolyte batteries, lithium-transition metal complex oxides are generally used, and Co, Mn, Ni, and the like are used as a transition metal. In recent years, spinel type lithium manganate and olivine type compounds such as olivine type lithium iron phosphate and olivine type lithium manganese phosphate are studied as inexpensive and highly safe positive electrode materials.
Since the olivine type compounds are low in electron conductivity or lithium ion conductivity, it has been difficult to obtain good charge/discharge properties. As technologies for enhancing the charge/discharge properties of olivine type compounds, there are studied carbon coating for enhancing the electron conductivity; reduction of a lithium diffusion distance and micronization for increasing a reaction area; and the like.
Embodiments described herein provide an active material for batteries having excellent charge/discharge performance and rate properties, a nonaqueous electrolyte battery containing this active material and having excellent charge/discharge performance and rate properties, and a battery pack provided with this nonaqueous electrolyte battery.
According to one embodiment, a positive electrode active material includes LiMn1-xMxPO4 (wherein M represents at least one element selected from Mg, Fe, Ni, Co, Ti, and Zr; and 0≤x<0.5) and has an average pore diameter of 8 nm or more and not more than 25 nm and a total pore volume of 0.05 cm3/g or more and not more than 0.3cm3/g.
According to another embodiment, a nonaqueous electrolyte battery includes a negative electrode containing a negative electrode active material, a positive electrode containing the positive electrode active material according to the embodiment, and a nonaqueous electrolyte.
According to still another embodiment, a battery pack includes the nonaqueous electrolyte battery according to the embodiment.
Examples of related art include JP-A-2008-034306 and JP-A-2008-184346.